Inductively powered devices

ABSTRACT

An inductively powered device comprises a memory tag ( 13 ) and an additional functional device ( 10 ) for powering by and communication with a reader device ( 11 ) emitting radio frequency signals. The inductively powered device is adapted such that when the memory tag ( 13 ) is powered by a reader device ( 11 ), the additional functional device ( 10 ) is also powered by the reader device ( 11 ) and carries out its function.

This application claims priority from Great Britain patent application0521835.9, filed Oct. 27, 2005. The entire content of the aforementionedapplication is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to inductively powered devices. In particularembodiments, it relates to inductively powered displays, to inductivelypowered displays associated or used with inductively powered memorytags, or to inductively powered devices associated with inductivelypowered memory tags.

BACKGROUND TO THE INVENTION

Transponder devices respond to an input signal by giving an outputsignal in response. The input signal, in many classes of transponder,serves to power the transponder. A widely used form of transponderdevice is the RFID tag—radio frequency power from a reader device isreceived by an antenna of the RFID tag. The RFID tag is powered andemits data in the form of an identifier by modulation of the powerreceived. The present applicants have proposed forms of transponderdevice, powered in a similar manner to RFID tags but designed to be readat short range and with memories for storing significant digitalcontent. Data storing transponder devices of this general type are heretermed memory tags—RFID tags may be considered a more limited form ofmemory tag than that discussed in more detail below proposed by thepresent applicants.

Data provided in memory tags is typically displayed in displays forminga part of reader devices used to power and read data from or write datato memory tags. While this is satisfactory for many use contexts, it isnot appropriate to all use contexts—particularly when it is desired fora party other than a user controlling a reader device to have access toor control over data stored in a memory tag.

SUMMARY OF THE INVENTION

In a first aspect, the invention provides an inductively powered devicecomprising a memory tag and an additional functional device for poweringby and communication with a reader device emitting radio frequencysignals, adapted such that when the memory tag is powered by a readerdevice, the additional functional device is also powered by the readerdevice and carries out its function.

DESCRIPTION OF DRAWINGS

Specific embodiments of the invention will now be described, by way ofexample, with reference to the accompanying drawings, of which:

FIG. 1 shows elements of a display suitable for use in embodiments ofthe present invention;

FIG. 2 shows a display device and a powering device according to anembodiment of the present invention;

FIG. 3 shows a memory tag and a reader device suitable for use inembodiments of the present invention;

FIG. 4 shows a physical appearance of the memory tag of FIG. 3;

FIG. 5 shows a display device, a memory tag, and a reader deviceaccording to an embodiment of the present invention;

FIG. 6 illustrates a method for communication between a reader device onthe one hand and a memory tag and a display device on the other handaccording to an embodiment of the invention;

FIG. 7 shows a biometric sensor, a memory tag, and a reader deviceaccording to an embodiment of the present invention; and

FIG. 8 illustrates a method for reading protected data from a memory tagby obtaining biometric readings from a biometric sensor according to anembodiment of the invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Elements of exemplary conventional display functionality will first bedescribed with reference to FIG. 1 so that elements of embodiments ofthe invention described further below may be placed in an appropriatecontext.

In such exemplary conventional display functionality, input logic 1receives control signals and responds to these control signals tooperate a display driver 2. The display driver provides display datasignals appropriate to drive the display element or elements 4. Datadefining an image for display is either received at the input logic 1and in most arrangements stored in a memory 2, or in other arrangementsis provided directly to the memory 2. The memory 2 is shown here as oneelement—in practice, multiple memories may be employed in a displaysystem (a main memory storing a whole image or a series of images, and abuffer memory for storing display data signals for providing to thedisplay elements themselves). Data for display and control signals(which may be provided together and interpreted by the input logic 1)are provided to the display functionality. Control and data for displayare provided to the display driver 3 (generally a conventional circuitdesigned for specific display elements) in a form in which it can thenprovide display data signals to the display element or elements 4 todisplay the image described by the data.

For an extremely simple display, as is appropriate to some embodiments,it will be possible to dispense with some of these functional elements.For a one-pixel, on/off, display, no memory 2 would be needed, and theinput logic 1 may amount simply to detection of when the display element4 should be activated (in such a case, input logic 2, display driver 3and even display element 4 could be combined together in simplecircuitry). For a two-dimensional multipixel display with multivaluedpixels, the elements shown in FIG. 1 are appropriate.

Input logic 1 may be comprised in a processor that has other functionsin the device of which the display functionality forms a part.Alternatively, input logic 1 may itself be downstream of a mainprocessor.

In the description of the embodiments of the invention that follow,display functionality will be shown as a functional block—reference backto FIG. 1 is appropriate for further consideration of the elements ofthat functional block. Exemplary display technologies, or technologyconstraints, will be described for the embodiments that follow. Theperson skilled in the art will thus appreciate how conventional displaytechnologies can be employed to produce embodiments of the invention asdescribed below.

FIG. 2 shows an inductively powered display device 20 according to anembodiment of the invention, together with a powering device 21 whichprovides both power and data for display to the display device 20.Provision of power and data is comparable to that used in RFIDtechnology—described in many reference sources, for example “RFIDHandbook”, Klaus Finkenzeller, 1999, John Wiley & Sons. The arrangementshown here is designed to for the display device to be powered atrelatively close range (near-contact) by the powering device and fordata to be rapidly transmitted between them—data can thus be providedfor display by “brushing” the powering device across the display device.

The display device 20 comprises a resonant circuit part 32 and arectifying circuit part 33, together with display functionality 24. Theresonant circuit part 32 comprises an inductor L2 shown at 35 and acapacitor C2 shown at 36 connected in parallel. The rectifying circuitpart 33 comprises a diode D1 shown at 40 connected to the resonantcircuit part 32 in a forward biased direction and a capacitor C4 shownat 41 connected in parallel with the components of the resonant circuitpart 32. The rectifying circuit part 33 operates as a half-waverectifier to provide power to display functionality 24.

The powering device 21 comprises a resonant circuit part 51 whichcomprises an inductor L1 shown at 52, in this example an antenna and acapacitor C1 shown at 53 connected in parallel. A signal generator 54 isconnected to the resonant circuit part 51 to provide a drive signal. Anamplitude modulator is shown at 61 operable to control the amplitude ofthe drive signal supplied from the frequency generator 54 to theresonant circuit part 51. A control unit 62 is operable to control theamplitude modulator 61 to provide data signals comprising control dataand image data for display to the display device 20 and hence to thedisplay functionality 24.

For the arrangement described above, it is particularly suitable to usedisplay technologies which have a low power demand (such as low powerCMOS) and which have very little latency on being powered on. For othercontexts (for example, where near-contact is not required and thepowering period may thus be longer), a broader range of technologies maybe suitable. If the powering device is left in extended communicationwith the display device, series of images (or even video) could bedisplayed using this approach. Embodiments of the invention may useeither traditional monostable displays which need to be refreshed, orbistable or monostable displays which do not require this. Both types ofdisplay, and their application for embodiments of the invention, aredescribed briefly below.

A suitable traditional monostable display technology would be low powerCMOS liquid crystal display (LCD). To maintain a positive image value,each LCD pixel element needs to receive a refresh signal at a regularinterval. If the display technology unit is unpowered, there will be noimage shown on the LCD display. In embodiments of the inventionutilising conventional LCD display technologies, an image is shown onthe LCD display only when power is provided—for a “brush and go” designsuch as that described in FIG. 2, this would mean that the image wasonly briefly visible. This may be advantageous in certain contexts—forexample as a visual indication to be provided, privately, to the user ofthe powering device alone. This use is more apparent when the display isused together with a memory tag (as is described in further embodimentsbelow). It should be noted that for this use, the image data need not beprovided by the powering device, but may instead be stored in a memoryof the display functionality unit. In such cases, it may not even benecessary for any signal to be provided by control unit 62—simplepowering of the display device 20 is sufficient to result in the storedimage being displayed. Alternatively, the stored image may only bedisplayed if particular control data is received from the poweringdevice 21—in such an arrangement, the stored image may be displayed onlyto authorised viewers provided with a control code to be provided toinput logic of the display functionality. Where a stored image of thiskind is held by the display device 20, it is necessary for at least apart of the memory used by the display device 20 to be non-volatile sothat the image data may be stored even when the display device isunpowered. Where there is no stored image, embodiments may or may notemploy non-volatile memory (it may be desirable to use non-volatilememory to store aspects of the input logic) but may retain image data involatile memory.

Alternative bistable or multistable display technologies do not requirerefreshing in this manner. A pixel element has more than one stablestate, the different display states having different image values, so animage may persist even if the elements are unpowered simply by ensuringthat different pixel elements are in different ones of their stablestates. Suitable commercially available technologies are the BiNemtechnology of Nemoptic of Magny les Hameaux, France, and the E Inktechnology of E Ink Corporation, Cambridge, Mass., USA. Again, it isdesirable in the context described for FIG. 2 for the technology to havelow power requirements and to have little latency on power up, but asbefore, these requirements are dependent on context. In thisarrangement, the displayed image persists even when the display deviceis unpowered. In such an arrangement, even a relatively simple displaymay have a range of different uses. For example, a powering device mayprovide image data personalised to a user so that the display devicereveals the user's name after being powered by the powering device—thismay be used to indicate that the user was the last person to read adocument on which the display device was mounted, for example.Alternatively, a display device could be mounted in a library book, andon checking out of the book, a librarian's powering device could writethe return date into the display device.

In further embodiments of the invention, display devices such as thatdescribed above with reference to FIG. 2 are provided in conjunctionwith memory tags. Memory tags suitable for use with embodiments of theinvention will now be described with reference to FIG. 3, which alsoshows a reader device analogous to the powering device of FIG. 2 forreading data from the memory tag.

Most generally, a memory tag is a passive electronic circuit powered bya reader device and containing a non-volatile memory in which data isstored. Generally, memory tags are inductively powered by RFtransmissions—the best known examples are RFID tags as described above.A further type of memory tag, suitable for near-contact reading withhigh data rate transmission, is described below. Elements of memory tag30 which are directly analogous to those of display device 20 are notdescribed further below—similarly, elements of reader device 31 whichare directly analogous to those of powering device 21 are not describedfurther below.

As for the display device 20, the tag 30 comprises a resonant circuitpart 32 and a rectifying circuit part 33, now together with anon-volatile memory 34. The resonant circuit part 32 further comprises acontrollable capacitive element generally indicated at 37, in theexample of FIG. 1 comprising a capacitor C3 shown at 38 and a switch S1shown at 39. The memory 34 comprises a data store generally illustratedat 45 comprising a plurality of data units 46. A program 49 controls thebehaviour of the memory tag.

In addition to the elements described above, the reader 31 furthercomprises a demodulator, generally shown at 55. The demodulator 55comprises a splitter 56 connected to the frequency generator to splitoff a part of the drive signal to provide a reference signal. A coupler57 is provided to split off part of a reflected signal reflected backfrom the resonant circuit part 51, and pass the reflected signal to amultiplier shown at 58. The multiplier 58 multiplies the reflectedsignal received from the coupler 57 and the reference signal receivedfrom the splitter 56 and passes the output to a low pass filter 59. Thelow pass filter 59 passes a signal corresponding to the phase differencebetween the reference signal and the reflected signal to an output 60.An amplitude modulator is shown at 61 operable to control the amplitudeof the drive signal supplied from the frequency generator 54 to theresonant circuit part 51. The control unit 62 is operable to receive theoutput 60 from the low pass filter 59 and validate the received data.

A signal comprising a data unit is transmitted to the reader 31 byoperating switch S1 shown at 39. This varies the resonant frequency ofthe resonant circuit part 32. This change in resonant frequency causesthe phase of the signal reflected from the resonant circuit part 51 tovary with respect to the signal provided by the signal generator 54.This relative phase shift can be processed by the multiplexer 58 and lowpass filter 59 to produce a digital output 63 as described in ourearlier co-pending application published as GB2395628A.

When the tag 30 is moved sufficiently close to a reader 31 so thatinductive coupling can be established between the resonant circuit parts51, 32, power will be supplied to the memory 34 to run the program 49and render the tag operational. A central part of tag operation is totransmit the data units 46 held in the data store 45. These are readfrom the data store 45 and transmitted as a part of a packet byoperation of switch S1 under operation of the program 49.

It is particularly desirable that the tag 30 be provided as anintegrated circuit, for example as a CMOS integrated circuit. Aschematic of such an integrated circuit is show at 80 in FIG. 2. Theinductor L2 is shown at 35, here as an antenna coil having only a singleturn although any number of turns may be provided as appropriate. Thecapacitor C4 is shown at 41, and the remaining components of theresonant circuit part and rectifying circuit part 33 are shown at block81. The memory is shown at 34. The memory 34 provides 1 Mbit of capacityof non-volatile memory and is of an area of approximately 1 mm2, anduses FRAM (ferroelectric random access memory) or MRAM (magnetoresistiverandom access memory) or similar memory technology requiring low power.The memory tag 30 is of a substantially square shape in plan view withan external dimension D for the sides of around 1 mm.

FIG. 5 shows an embodiment in which the display device of FIG. 2 and thememory tag of FIG. 3 are collocated to form a composite device. Readerdevice 11 has the elements of reader device 31 shown in FIG. 3—it hascapacity both to receive data from a memory tag and to send data to adisplay device (and also to the memory tag, in some embodiments). Thememory tag 13 and the circuitry 12 of the display device 10 (other thanthe display elements 15) are stacked over each other such that readerdevice 31 will power both the memory tag 13 and the display device 10 atthe same time (the skilled person will appreciate in individual designcontexts how this functional task may be achieved most effectively).This display device circuitry 12 is essentially similar, physically, tothe physical elements of the memory tag 13 as shown in FIG. 4. Thedisplay device 10 and the memory tag 13 differ essentially only in thedisplay elements 15—these are disposed to the side of the circuitry 12and memory tag 15 so that these can be seen even when the reader 11 ispowering the display device 10 and the memory tag 13. The substrate 14on which all these components are mounted may be effectively anysubstrate in which a use for the composite device may be found: adocument; product packaging; a wall of an electrical appliance;virtually any other non-perishable physical product. Use models of sucha composite device as this are discussed briefly below.

In the arrangement shown in FIG. 5, the memory tag 13 and the displaydevice 10 are separate components that are collocated but which do notdirectly interact, communicating only through the reader device 11. Amethod for providing images from data in the memory tag is set out inFIG. 6. It should be noted that an alternative arrangement—as describedin the discussion of FIG. 2—is for memory tag and display devicefunctionality to be combined in a single device. However, where highspeed and low power operation is necessary, it may be advantageous toprovide two relatively simple devices interacting through a readerdevice (which itself may have far less limiting power and speedconstraints) rather than one relatively complex device.

As shown in FIG. 6, the first step 101 is to power up the memory tag andthe display device by bringer the reader device into sufficiently closeproximity to both. Once the memory tag is powered up, it will providedata to the reader device in the second step 102 by modulating theimpedance of the memory tag in the manner described with respect to FIG.3. This data consists of, or contains, or possibly simply references, animage to be displayed on the display device. The reader device then, inthe third step 103, prepares data to send to the display device. If thememory tag simply holds data in a form usable directly by the displayfunctionality of the display device, this step may not be necessary atall. However, if the memory tag only contains a reference to image data,or data in a form not itself adapted for display by a display device(for example, a file in a word processing format, or even in a displayformat such as TIFF), the necessary processing step is most effectivelycarried out at the reading device, which can readily be provided with ageneral purpose processor and the capability to run all necessaryapplications. In the fourth step 104, data is provided to the displaydevice. For a combined memory tag and display device with a read-onlymemory tag, this may be achieved straightforwardly—all data sent out bythe reader device may be simply display data. However, embodiments whichcombine a display device with a memory tag which may be written to aswell as read from are perfectly possible. In this case, relevant logicof both the memory tag and the display device need to be able todiscriminate data which is relevant to their device from other data.This may be achieved by using packetised data with headers. The relevantlogic does not read data unless it detects a particular header valuewhich indicates that that packet is relevant to that particular device.Where the particular header is detected, that packet is read. Where thatparticular header is not detected, the relevant logic simply waits forthe next packet and performs the same assessment. In the fifth step 105,the display driver of the display device generates display data signalsfrom the data sent to it by the reader device: for a conventionalmonostable device, these display data signals are fed with refreshsignals to the display elements for as long as the display device ispowered; for a bistable or multistable device display data signals areprovided to the display elements to replace the existing displayed imagewith a new image.

In other embodiments of the invention, another functional device ratherthan (or even as well as) as a display can be collocated with a memorytag to provide a new form of composite device. Such a functional devicemay be another output device as an alternative to (or in addition to) adisplay, such as a loudspeaker. Again, a low power CMOS component couldeffectively be used, and similar approaches could be employed forproviding signals to a loudspeaker as are described above for providingsignals to a display.

The other functional device need not be an output device—it may insteadbe an input device. An example is shown in FIG. 7. A circuit device 110comprises a memory tag overlaid with the circuitry of a fingerprintreader. The fingerprint reader circuitry is connected by wire to thereader pad 111 of the fingerprint reader—this may be a low power CMOSfingerprint reader (examples of CMOS fingerprint readers are widelyavailable). A legend 112 indicates that protected information in thememory tag will be made available on use of the fingerprint reader whilepowering the memory tag.

FIG. 8 indicates a method for obtaining protected data from the memorytag. The memory tag and the fingerprint reader are both powered up (121)by moving a reader device into proximity with the antennae of thedevices. The reader device reads data from the memory tag (122) anddiscovers that the memory tag holds protected data (unprotected data maybe simply read at this point—this may provide a visual indication to theuser that the fingerprint reader is needed, and may provide elements ofa user interface for the fingerprint reader). The reader device thenobtains (123) a fingerprint measurement from the fingerprint reader(which may, for example, simply obtain a measurement as soon as it ispowered up, or on response to a signal from the reader device). Thismeasurement is sent (124) to the memory tag, and the logic of the memorytag determines (125) whether the measurement is a satisfactory match toinformation relating to allowed fingerprint users that it holds.Alternatives are possible—for example, it may be that the fingerprintreader allows access to all users who provide a fingerprint, but thenstores that data in the memory tag to provide an access log. If themeasurement is satisfactory (126), the protected data is returned to thereader device. If it is not satisfactory (127), an error message isreturned instead.

As for output devices, a variety of different input devices could beused. A touchpad could be employed to provide a confirmation of physicalpresence at the spot, or even to provide digitised input. A similarapproach for providing interaction between the input device and thememory tag could be employed as for the biometric reader and the memorytag described above.

Although embodiments of this invention have been described with respectto a specific memory tag technology, the skilled person will appreciatethat other memory tag technologies may be used both for the memory tagitself and in modification for powering and providing data to a displayor other functional device.

1. An inductively powered device comprising a memory tag and anadditional functional device for powering by and communication with areader device emitting radio frequency signals, adapted such that whenthe memory tag is powered by a reader device, the additional functionaldevice is also powered by the reader device and carries out itsfunction.
 2. An inductively powered device as claimed in claim 1,wherein the additional functional device is an output device.
 3. Aninductively powered device as claimed in claim 2, wherein the additionalfunctional device is a display, and the display carries out the functionof displaying data transmitted to it by the reader device.
 4. Aninductively powered device as claimed in claim 3, wherein the datatransmitted to the display is derived from data stored on the memorytag.
 5. An inductively powered device as claimed in claim 3, wherein animage displayed by the display is provided only while the display ispowered by the reader device.
 6. An inductively powered device asclaimed in claim 3, wherein the display is a bistable or multistabledisplay and the image displayed by the display is provided only whilethe display is powered by the reader device.
 7. An inductively powereddevice as claimed in claim 1, wherein the additional functional deviceis an input device.
 8. An inductively powered device as claimed in claim1, wherein the additional functional device is a biometric reader whichtakes a measurement while the biometric reader is powered by the readerdevice.
 9. An inductively powered device as claimed in claim 8, whereinat least some data in the memory tag is only provided to the reader ifthe reader provides the measurement from the biometric reader and themeasurement meets predefined criteria.
 10. An inductively powered deviceas claimed in claim 8, wherein the biometric reader is a fingerprintreader.
 11. A display device powered by radio frequency communication,the display device comprising: an antenna and an induction circuit forobtaining power from radio frequency transmissions provided by apowering device; display driver circuitry for providing a display datasignal to a display; and a display for displaying an image according tothe display data signal.
 12. A display device as claimed in claim 11,wherein the display device comprises a memory, and wherein the displaydata signal is derived from data stored in the memory.
 13. A displaydevice as claimed in claim 12, wherein the powering device provides dataas well as power in the radio frequency transmissions, and this data iswritten to the memory.
 14. A display device as claimed in claim 11,wherein the image is displayed only while the display device is poweredby the powering device.
 15. A display device as claimed in claim 11,wherein the display is a bistable or a multistable display, wherein theimage may be changed only when the display device is powered by thepowering device but is still displayed even when the display device isnot powered by the powering device.
 16. A bistable or multistabledisplay device comprising an antenna, an induction circuit for obtainingpower and data from radio frequency signals, a display driver forproducing display data signals from the data, and a bistable ormultistable display for displaying an image and for modifying the imagein response to the display data signals, wherein the image is displayedwhether or not the bistable or multistable display device is powered butis modified only when the bistable or multistable display device ispowered.
 17. A bistable or multistable display device as claimed inclaim 16 and further comprising a memory, wherein the data is writteninto the memory from the induction circuit and provided to the displaydriver from the memory, whereby the image displayed by the bistable ormultistable display corresponds to the data held in the memory.
 18. Amethod of displaying data stored in a memory of an inductively poweredmemory tag, comprising: a reader device providing radio frequencysignals to the inductively powered tag with to power the inductivelypowered tag and to read data from the memory; the reader device poweringan inductively powered display device and providing data for displayderived from the data read from the memory to the inductively powereddisplay device, whereby an image is displayed on the inductively powereddisplay derived from the data in the memory.
 19. A method as claimed inclaim 18, wherein the image is displayed only while the reader device ispowering the inductively powered display device.
 20. A method as claimedin claim 18, wherein the inductively powered display device is abistable or multistable inductively powered display device and the imageis displayed whether or not the reader device is powering theinductively powered display device but is changed only when readerdevice is powering the inductively powered display device.
 21. A methodof providing authenticated access to data stored in a memory of aninductively powered memory tag, comprising: a reader device powering aninductively powered biometric reader which takes a measurement while thebiometric reader is powered by the reader device and provides themeasurement to the reader device; the reader device providing radiofrequency signals to the inductively powered tag with to power theinductively powered tag, to provide data derived from the measurement tothe inductively powered tag and to read certain of the data from thememory if the data derived from the measurement matches predefinedcriteria.